Interlocking circuits



J anr.-17; 1939.

.o. H. SCHADE IN TERLOCKING CIRCUITS Original, File d Dec. 15, 1933 INVENTOR OTTO H. CHADE ATTORNEY Patented Jan. 17, 1939 PATENT OFFICE IN TERLOCKING CIRCUITS Otto H. Schade, West Orange, N. J., assignor to Radio Corporation of America, a corporation of Delaware Original application December 15, 19 33, Serial No. 702,451. Divided and this application August 9, 1935, Serial No. 35,512

7 Claims.

The present invention relates broadly to energizing circuits for amplifiers utilizing electronic tubes and more particularly to novel interlocking circuit arrangements for bias rectifiers. This application is a division of my co-pending application #702,451 filed December 15, 1933, now,

U. S. Patent No. 2,037,659.

Vacuum tube amplifiers require supply voltage sources for input (C-bias voltage) and output (B-voltage) circuits that are substantially independent of one another, at least within the ampli fied frequency range. monly used to prevent A. C. reactionsbetween B and C voltages if both are taken from a single supply source. In the case of very low frequency amplification these filter networks assume large proportions and finally cease to operate at zero frequency.

Class B operation of amplifier tubes at varying signal intensities, such as in broadcasting, causes considerable variation of the B supply current which in turn causes fluctuations of the B supply voltage, The magnitude of these fluctuations depends upon the internal resistance of the B supply source. It is well known that variations of the C bias voltage of amplification has a considerably greater effect on the performance of the amplifier than variations of the B voltage. Obviously then, when the same source is utilized for the C and B voltage supply slight variations in the C bias voltage caused by variations of the B supply current produce undesirable efiects. Superior results are, therefore, obtained with biased low frequency amplifiers, especially, those 3 of the over-biased type (Class AB or Class B) if a separate voltage supply system for bias voltages is provided. In accordance with the present invention the bias voltage is conveniently supplied from a separate rectifier circuit. The power required is'usually small so that a vacuum tube rectifier of relatively low saturation current may be used successfully for this purpose.

In a particular practical embodiment of the invention it was found that utilizing one diode contained in a type 55 amplifier tube gave commendable results. If a separate rectifier tube or diode is used to furnish bias voltage to other amplifier tubes it is necessary to provide means for interlocking the bias rectifier and the other amplifier tubes in such a way that removal of the rectifier tube andthus taking off the-bias voltages,

does not cause destructions in the tub-es normally receiving bias voltage from this rectifier.

Objects of the invention are to provide simple but effective interlocks between the biased tubes Filter networks are comand the bias rectification circuits so that the power tubes may be protected should the bias rectifier burn out or be removed as when replaced. Still other objects of the invention are to improve generally the simplicity and efficiency of energizing circuits for vacuum tubes and particularly to provide an economical and compact form of bias rectifiers and interlocking arrangements for amplifier circuits and the like which is not only reliable in operation but may be economically manufactured and assembled. The novel features which are believed to be characteristic of the invention are set forth in particularity in the appended claims.

The invention itself, however, both as to its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which there is indicated diagrammatically several circuit arrangements whereby the invention may be carried into effect.

In the drawing, Figure 1 illustrates a form of the invention applied to a pair of power tubes in push-pull, containing diodes which are used for C bias purposes, the bias voltage interlock being provided in the power tubes themselves;

Figure 2 illustrates another modification of the broad principle illustrated by Figure 1 and providing better results; and,

Figure 3 illustrates a modification of the invention wherein a separate bias rectifier of the full wave type is used and wherein the tubes to be biased become self-biased if the separate bias rectifier is removed at which time the filament circuit of the power tubes is opened.

roadly construed the invention described in said (ac-pending application #702,451 provides three methods of protective interlocks. The first of these methods which is illustrated generally by Figure 1 of said co-pending application provides a bias rectifier and plate voltage rectifier enclosed within a single envelope. The cathodes of both of these rectifiers are heated by the same current. In other words, the heating circuits are in series. The interlock is provided by reason of the fact that one of the rectifiers cannot be removed without the other since they are both within a single enclosure; also a burn-out of the heater will affect both rectifiers simultaneously, since, as previously stated, the heating circuits are in series and the same current traverses both thereof.

The second method utilizes a bias rectifier (diode) which is contained in the envelope of the tube receiving the bias voltage. Both Figures 2 and 3 of the copending application (Figs. 1 and 2 of the present divisional application) illustrate this method. It is quite obvious from a consideration of the drawing that the bias rectifier cannot be removed without removing the tube and further that a heater burn-out affects both the bias rectifier and the tube receiving the bias voltage since they both have the same cathode.

The third method incorporates a separate bias rectifier tube and is illustrated generally by Figure 4 of the copending application (Figure 3 of the present divisional application). The interlock in this case is provided by means of a socket contact opening the filament circuit of the biased tubes and removing a short-circuit across a self-bias resistor. The socket contacts are made by one of the heater pins of the bias rectifier in connection with two auxiliary pins thereof. On removal of the bias rectifier tube a self-bias resistor is, so to speak, thrown in and provides a bias voltage for the tubes. At the same time the filament circuit of these tubes is opened so that the cathodes thereof become cold or at least have a lower temperature when the bias rectifierv is re-installed in the socket. In this arrangement as the bias rectifier does not provide a bias voltage until its cathode starts to emit, the amplifier tubes may draw relatively heavy plate currents if the biased rectifier is quickly replaced by a cold tube (the self-bias resistor is shortened when the bias rectifier is inserted) hence, the bias rectifier tube should have a short heating time so as to shorten the time of overload current on the amplifier tubes to a minimum.

However, it has been found in practice that an exchange of the bias rectifier tube requires sufficient time to lower the emission of the amplifier tubes sufficiently to prevent severe overload currents.

It should be understood that while the energy for the bias voltage rectifier has been shown as derived from the commercial power supply mains or power transformer it should be understood that any suitable source may be utilized for this energy, as for instance, the local oscillator in superheterodyne receivers.

The interlock in the case of Figure 1 of the parent application is provided by reason of the fact that the bias rectifier which is shown as the half wave rectifier cannot be removed without removing the B supply rectifier or the full wave rectifier. Also, in view of the fact that the heater circuits are connected in series a burn-out in one will necessarily disable the other as previously disclosed.

While the tube T1 of the parent application Serial No. 702,451v has been shown as comprising a full wave rectifier and a half wave rectifier, it is to be distinctly understood that the tube may comprise two full wave rectifiers or two half wave rectifiers and that the arrangements of B supply and C supply may be reversed, that is to say, the B supply may be derived from a half waverectifier whereas the C bias supply may be derived fromthe full wave rectifier.

In Figure 1 of the present application the power transformer PT is provided with a primary 3 and two secondaries 25 and 26. Primary 3 is adapted to be connected to the mains of commercially available alternating current by means of the terminals I and 2. A full wave rectifier T2 is provided with a cathode connected across the secondary 25 and two anodes connected respectively to opposite ends of the secondary 26.

The midpoint 2! of secondary 26 is grounded as at G. A push-pull amplifier including a pair of electronic tubes T3 and T4 of any type of amplifier circuit is shown energized by the full wave rectifier T2. Tube T3 is provided with the usual anode, cathode and control electrode and in addition a diode plate 45. Tube T4 is similarly constructed in that it is provided with an anode, cathode and control electrode and a diode plate 46.

The anodes of tubes T3 and T4 are respectively connected to opposite ends of the primary of an output transformer 42, the secondary of which is connected to a suitable translating device or the like. The cathode point of the rectifier T2 is connected through a suitable filter choke 32 to the midpoint of the primary winding of transformer 42. This connection is provided so that the anodes of tubes T3 and T4 may be supplied with the necessary energizing potential. Filtering of this potential is performed by the filter circuit comprising choke 32 and grounded condensers 30 and 3| in customary fashion. The input to the tubes T3 and T4 is provided by means of an input transformer having a primary winding and a secondary winding, the energy to be amplified being applied across terminals 33 and 34 of primary winding 35 of the input transformer, the opposite ends of the secondary winding of the transformer being connected respectively to the control grids of tubes T3 and T4 as shown. A common portion of the input circuit of both tubes T3 and T4 connects both cathodes 43 and M to the midpoint of the secondary winding through a pair of resistors 3'! and 38.

Diode anode 45 is connected directly to diode anode 46 and a common connection from both diodes is provided through a condenser 29 to a point 28 of the secondary 26. The cathode end of. the resistor 38 is grounded as at G while a suitable condenser 39 is connected between the secondary end of the resistor '31 and ground.

From the above it can be seen that an alternating current as derived across portion 21, 28 of secondary 26 is impressed across the resistor 38 and that this alternating current is rectified in one instance by the action between diode anode 45 and cathode 43 and in another instance between the action of diode plate 46 and cathode M. It is also evident that the resistor 38 is in the grid circuits of both tubes T3 and T4, hence, the drop across the resistor 38 caused by the fiow of uni-directional current therein is utilized to bias the control grids of the two push-pull tubes. Resistor 3'! and condenser 39 are provided so as to form a filter circuit which acts to attenuate the ripple voltage, hence, producing a smooth bias voltage for the two push-pull tubes.

The necessary heating current for the heating circuits of cathodes 43 and 44 is connected to terminals 49 and ii in any suitable manner.

As previously inferred the interlock in the case of Figure 1 is provided by reason of the fact that the bias rectifier is within the same envelope as the amplifier tube hence it cannot be removed without removing the amplifier tube itself. Also, heater burn-outs affect both simultaneously. Whereas, the invention in Figure 1 has been described in connection with a pair of tubes in push-pull it is obvious that any other type of amplifier circuit may be employed as, for instance, a single amplifier tube.

Figure 2 is somewhat similar to the arrangement shown in Figure 1 except that the bias voltage is derived across a resistor 50. For this purpose the power transformer PT is provided with an additional secondary winding 52; one end of which is connected to .the center point of the secondary 35 of the input transformer, while the other end is connected to both diode anodes 45 and 4.6 of tubes T3 and T4 respectively. The common cathode connection of the two tubes is shown grounded as at G. A connection is provided from the first mentioned end of secondary 52 to ground, this connection including a bias resistor 50 shunted by. a by-pass condenser 49. From a study of Figure 2 it will be seen that the alternating current derived across the secondary 52 is rectified bythe diode rectifiers 45, 43 and 46, 44 thereby causing the'rectified current to pass through the resistor '55. This resistor is connected in the grid circuits of both tubes T3 and T4, hence, supplying the necessary bias voltage. Condenser 4b is utilized so as to by-pass the applied A. C. voltage so as not to develop a large ripple voltage component across the resistor 50.

In the system shown in Figure 2 the interlock is provided in the same manner as described in connection with Figure 1 and it is to be understood that the system shown in Figure 2 may be applied equally well to a single tube amplifier arrangement in place of the push-pull circuit shown.

In Figure 3 a biasing rectifier tube T7 is provided having four pins 52, 63, 64 and 65. The pin 62 and 63 are utilized to feed energy to the heating element 5!. Cooperating with the heating element 6| are two cylindrical cathodes 51 and 58, these being. connected to points 55 and 54 respectively of the secondary 26. The midpoint 55 of the secondary 25 is grounded as at G. Tube T7 is also provided with a pair of anodes 59 and 60. Anode 59 cooperates with the cathode 58, whereas, anode 50 cooperates with the cathode 51. The two anodes are connected together and by a common conductor B3 are connected to midpoint of the secondary 36 of input transformer. The biasfor the tubes T5 and T6 is provided by reason of the fact that the drop across the bias resistor i2 is impressed upon the grid circuits of the tubes T5 and T6. The rectifier tube T7 may be considered as a full wave rectifier in inverse relation to the rectifier T2- so that the potentials developed by the rectifier T7 are negative and may be utilized for biasing purposes. Condenser H is provided to by-pass the applied A. C. voltage so that it does not develop a large ripple Voltage across resistor F2. The proportion between terminals 56 and 54 of secondary 28 is utilized for feeding the A. C. to the cathodes 57 and 5B of rectifier T7. The secondary 53 is utilized to furnish current to the heater of tubes T5 and Te as well as to the heater element 6! and is additionally provided with terminals 56 and 61 for feeding energizing currents to any other heaters of the system. A selfbias resistor 15 is connected across the connections 59 and H! from pin terminals 54 and #555 respectively so that upon removal of the tube T1 from its socket the resistor 15 comes into play as a self-bias for the tubes T5 and Tc and thus prevent damage to the tubes while the cathodes thereof remain hot. It should be noted that removal of the tube T: from its socket not only breaks the circuit at points 62 and 55 but also breaks the circuit at points 64 and $5 so that the short-circuit across resistor 15 is removed. When the tube T7 is again replaced in its socket a short-circuit is provided across the resistor 15, thus preventing its aifecting tubes T5 and T6.

The interlock in the circuit arrangement described in Figure 3 is provided by reason of the fact that the removal of tube Tmbreaks the filament circuit of the amplifier tubes T5 and T6 and further conditions resistor 15 so as to act as a self-bias to protect the tubes T5 and T6 while the cathodes thereof remain hot.

While there has been indicated and described certain specific arrangements for carrying the invention into effect it will be apparent to anyone skilled in the art that the invention is by no means limited to the particular organizations shown and described but that many modifications may be made Without departing from the scope of the invention as set forth in the appended claims.

I claim:

1. In a signalling circuit, a multiple function tube having an anode, a cathode, a grid electrode and a diode plate, said anode, cathode and grid electrode forming one section'of the tube and said cathode and diode plate forming another section of the tube, a pair of terminals adapted to be connected to an alternating current power supply line, a power conditioning circuit including a rectifier and filter arrangement interposed between said pair of terminals and the anode, cathode path of said tube for providing the tube with anode current, a circuit for connecting the diode plate cathodepath effectively across said terminals, said last named circuit including an impedance for developing a direct current potential, a conductive connection between a point of said impedance and a grid electrode of said tube, a signal input circuit for said tube comprising a signal energy transfer device connected between the grid electrode and the cathode thereof, and a signal output circuit including signal energy transfer means connected between the anode of said tube and said cathode thereof.

2. In a signalling circuit, a multiple function electronic tube having a plurality of sections, one

of said sections comprising an anode, a cathode and a grid electrode, another section comprising a diode plate and said cathode, a pair of terminals adapted to be connected to a source of alternating current, a circuit for connecting the anode, cathode path of the tube effectively across said terminals, a circuit for connecting the diode plate cathode path of the tube effectively across said terminals, said last named circuit including an impedance element for developing a direct current potential, a conductive connection between the grid electrode of said tube and the cathode thereof, said connection including at least a portion of said impedance, said impedance being arranged with respect to said conductive connection so that in operation of said signalling circuit the grid electrode is maintained at a negative potential with respect to the cathode.

3. In signalling apparatus and the like, a first space discharge device provided with an anode, a cathode and a grid electrode, a second space discharge device provided with an anode, a cathode, a grid electrode and a diode plate, a pair of terminals adapted to be connected to a source of alternating current, a power conditioning circuit including a rectifier and a filter unit interposed between said pair of terminals and the space paths of each of said tubes whereby said tubes are provided with space current, a circuit for effectively connecting the diode plate to one of said terminals and the cathode of said second space discharge device to the other of said terminals, said circuit including an impedance device for developing a direct current potential and a connection between the first named grid electrode and the first named cathode including at least a portion of said impedance device whereby the potential developed across said portion of the impedance device is applied between said last named cathode and grid electrode.

4. In signalling apparatus and the like, a pair of electronic tubes, connected in push-pull, each of said tubes being provided with an anode, a cathode, a grid electrode and a diode anode, the anode, cathode and grid electrode forming an r amplifying unit and the cathode and diode anode forming a rectifier unit, terminal means adapted to be connected to'a source of alternating current, means for connecting the diode units of ie two tubes to said terminal means; an impedance device connected between the diode anode and the cathode of each of said tubes, said impedance device being also included in a common portion of the push-pull input circuit.

5. In a signalling apparatus, an electronic tube having an anode, a grid electrode, a cathode and a diode plate, a source of alternating current, a rectifier circuit and filter connected to said source, said rectifier circuit and filter circuit being adapted to rectify the alternating current ,from said source to produce therefrom pulsating uni-directional current and to smooth out the pulsating uni-directional current, means for applying the smoothed uni-directional current between the anode and cathode of said electronic tube, means for impressing alternating current from said source between the diode plate and cathode of said electronic tube, a connection between said diode plate and cathode comprising a resistor element, a connection between the grid electrode and the cathode of said electronic tube, said last named connection including said resistor element.

6. In signalling apparatus and the like, a first electronic tube provided with anode, cathode, grid electrode and diode anode, a second electronic tube provided with anode, cathode, grid electrode and diode anode, a push-pull input circuit for said tube including a connection between the grid of the first tube and the grid of the second tube, said connection including the secondary of an input transformer, the primary of the input transformer being provided with means adapted to be connected to a source of signal energy, means connecting the cathode of the first tube to the cathode of the second tube, a connection between said last named means and a point in the vicinity of the center of the secondary of said transformer including a bias resistor and a filter resistor in series, a filter condenser connected between said point of the secondary winding of the transformer and ground, a connection between the diode anode of the first tube and the diode anode of the second tube and a point intermediate the bias resistor and the filter resistor, means connecting the two cathodes to ground, a connection between the anode of the first tube and the anode of the second tube, said connection including the primary of an output transformer, the secondary therefor being provided with means for connection to a utilizing device, a source of space current for said tubes comprising a rectifier having a pair of anodes and a cathode, a power transformer provided with a primary winding and a plurality of" secondary windings, means adapted to connect the primary "winding to a source of alternating. current, a cathode heating circuit connected across one of the secondary windings, means connecting one of the anodes of the rectifier tube to one end of another of said secondary windings and the other anode of the rectifier tube to the other'end of said last named secondary winding, means connecting a point in the vicinity of the electrical center of the last named secondary winding to ground, means for connecting a point of the last named secondary Winding other than the last named point thereof to said point intermediate the bias resistor and the filter resistor, said last named means including a condenser, means including a filter choke connecting a point in the vicinity of the center of the primary winding of said output transformer to the cathode of the rectifier tube, and a filter condenser connected between ground and a point of the last named means.

'7. In signalling apparatus and the like, a first electronic tube provided with anode, cathode, grid electrode and diode anode, a second electronic tube provided with anode, cathode, grid electrode and diode anode, a push-pull input circuit for said tube including a connection between the grid of the first tube and the grid of the second tube, said connection including the secondary of an input transformer the primary of the input transformer being provided with means adapted to be connected to a source of signal energy, means connecting the cathode of the first tube to the cathode of the second tube,

a connection between said last named means and a point in the vicinity of the center of the secondary of said transformer including a bias resistor, a filter condenser shunted across the bias resistor, a connection between the diode anode of the first tube and the diode anode of the second tube and said point of the secondary of the input transformer, means connecting the two cathodes to ground, a connection between the anode of the first tube and the anode of the second tube, said connection including the primary of an output transformer the secondary therefor being provided with means for connection to a utilizing device, a source of space current for said tubes comprising a rectifier having a pair of anodes and a cathode, a power transformer provided with a primary winding and a plurality of secondary windings, means adapted to connect the primary winding to a source of alternating current, a cathode heating circuit connected across one of the secondary windings, means connecting one of the anodes of the rectifier tube to one end of another of said secondary windings and the other anode of the rectifier tube to the other end of said last named secondary winding, means connecting a point in the vicinity of the electrical center of the last named secondary winding to ground, means including a filter choke connecting a point in the vicinity of the center of the primary winding of said output transformer to the oath-- ode of the rectifier tube, and a filter condenser connected between ground and a point of the last named means, said connection between the diode anodes and said point of the secondary oi the input transformer including another of the secondary windings of the power transformer.

O'I'IO H. SCHADE. 

